The connection between CO2 readings and covid

The connection between CO2 readings and covid is they measure the ventilation in the room. People generate CO2 as they exhale, talk, sing. If the room has good ventilation the CO2 is being cleared out and doesn’t accumulate. So, CO2 is a marker for how well the ventilation is working in the room.  This is the connection to covid. If the ventilation is clearing out the CO2, it’s also clearing out droplets that would contain covid virus if someone was infected.

A CO2 reading of 400-500 is a normal outdoor CO2 level.  We set the ventilation in the room for a reading in the low 500’s before singers arrive.   If the readings in the room move above 650 we increase ventilation until the numbers come down into the 500’s again.

Here is an article to read on the topic. You will see they set the levels much higher than we do at Mystic.

Can CO2 sensors be used to assess COVID-19 transmission risk?

ARTSBoston Lecture 6/10/2021

Joseph Allen, founder & director of the Healthy Buildings Program at Harvard University School of Public Health.   Allen has been working with American Repertory Theater since the start of the pandemic to develop a “Roadmap to Recovery” for arts organizations to develop science-based plans for reopening.

Overall Advice:
YES, it’s time to start coming back.
AND we have to stay on top of the science.
People will be ready at different speeds.
Expect tension & uneasiness.
Be flexible & dynamic in your planning.
Communicate with your people (singers & audience)
Hold town halls, answer questions, be as transparent as possible

Establish your organization’s “Guiding Principles”
I found this really important.  Before you discuss any specific policies/practices/strategies, define your guiding principles.  Many things will change, sometimes really fast.  What you decide today may not work in September.  But your guiding principles will give you the foundation for ongoing decision-making as things change.   His suggested guiding principles:

  1. Health and Safety First 
  2. “Layer the Defense” (Hierarchy of Controls). Do the most important things first:
    1. Virus Control: Vaccines*
    2. Engineering Controls: Ventilation, Filtration*
    3. Admin Controls: Spacing
    4. PPE Controls: Masks
    5. *Note: the better you do with the first ones, the less you have to do the others
  3. Timelines, Policies & Practice will be determined by the disease.
  4. We will stay flexible; we may need to change our policies and practices. 
  5. Psychology Matters.
    What science says is “safe” is not the same as how people feel.   Feeling safe will be different for different people.  Your organization needs to decide how to engage with this.  Arts organizations will lose subscribers for moving too fast AND for moving too slow.  You need to decide what’s right for you.


Your Audience

  • Your Audience will be knowledgeable; they will ask about vaccines & ventilation. Be ready.
  • If you have 100% vaccinated singers, say so. This will help with audience comfort.
  • If you know the ventilation stats on the performance hall, say so. This will help (if they are good).
  • You can ask audience if they are vaccinated when they purchase tickets. This will help you in planning decisions, like how to space seating.  If 95% of audience is vaccinated, great, no real need for spacing.  If not, you may decide to use spacing.

Requiring Vaccinations

Fully Vaccinated singers (and you have proof) in a room ventilated following the guidelines (CADR 350), do not need to wear masks or socially distance.  If an individual is vaccinated but compromised so that their body may not have made a lot of antibodies, they may want to wear a mask and distance.

For unvaccinated or status unknown performers (singers, wind instruments), insist on a rapid test each time they perform.

To have unvaccinated singers indoors, even masked, you must have EXCELLENT air flow.  Very risky.

For unvaccinated or undisclosed… “require a rapid antigen test within a few hours of every rehearsal and performance”.

in a large rehearsal hall, do they need to socially distance in the spacing?


Good indoor air quality is about bringing outdoor air inside.

The good news is the First Parish Sanctuary is easily adjusted to have good indoor air quality because it has a wall of windows that open and doors on opposing sides that open to the outside.  If the ventilation system does not have a high enough Clean Air Delivery Rate (CADR), then we must open windows and doors and place fans or air purifier systems (fans with HEPA filters) in the windows and doors.  Compare this to the concert hall at Tremont Temple where there are no windows that open, no doors that open to the outside in the hall, and the doors that do open to the outside are on a different floor.  This is a much harder problem to adjust if the ventilation system is inadequate.

We have to pay attention to small, enclosed spaces that we use; bathrooms, backstage spaces, band room, soloist room, Green Room at First Parish.  These are likely to have poor air quality, but easily fixed.  Put portable air purifier systems with H13 hepa filters in those rooms/spaces.  These are inexpensive ($50 to $150), small, and readily available in hardware stores.  You measure the room and then match the system to your size room.  I hope that First Parish would place these in their bathrooms.

H13 filter – This is a medical-grade air filter.  Common filters are H11 or H12.  H13 can trap smaller particles and with higher effectiveness (99.9% vs 85% to 95%).

Low cost solution ($50) – ordinary window fan blows through cardboard box lined with many H13 filters).

We want a CADR in our rooms of 350, very good, over 5 air changes per hour.

Clean air delivery rate (CADR) is listed on an air purifier system.

Clean Air Delivery Rate (CADR) of a room = CADR of an air purifier x 60 / volume of the room.  Add air purifier systems until you reach the CADR you desire.

A system that exchanges the air in a room up to 1,000 sq ft in one hour, 500 sq ft in 30 minutes, 250 sq ft in 15 minutes has a CADR of 250.

Yes, they create noise.  There are no quiet solutions on the market yet but some systems come with a quiet night mode.  Noise may be an issue during performances.

Old buildings can be easier to fix because they breathe.  They are drafty.

Updated CDC airflow guidelines.


Cleaning Surfaces

Cleaning protocols, how often, how much?

There are no documented cases of transfer of covid from surface to people (FOMITE).

Don’t need to clean surfaces.  Just hand sanitizer on table.

CDC says once a day cleaning of surfaces is fine.


“Baseline risk” – by area.  Mass is getting low.

When the official baseline risk in your area is low, you can drop a lot of protocols; masks, social distancing.


Unknown vaccination status. Masked?  Distanced?  Segregated (place unvaccinated people in a balcony, for example, separate from vaccinated audience members).

Distance between singers and audience.  Depends on vaccination status.  If all your singers are vaccinated, tell audience for psychological value.  They will appreciate knowing.

ASHRAE Standards and Guidelines

American Society of Heating, Refrigerating and Air-Conditioning Engineers


John Nix, MM; Professor of Voice and Voice Pedagogy, University of Texas/San Antonio, 210-458-5678

Air Changes per hour ACH  – 4-6 changes per hour recommended

Open the windows plus ventilation system

No less than a level 8 filter

Filtered air is a mix of fresh and recirculated air

If removing people periodically, allow 1 air change before returning.

Hepa – high efficiency particulate , refers to how efficient the filter is at removing particles from the air.


CADR – clean air delivery rate in cubic feet per minute, compare to volume of room.

Look for smoke.  It is the same size as virus particle, .3 microns

CFM Cubic feet per minute

CO2 level – goes up with more people so monitor this with carbon dioxide meter.  More fresh air makes this go down.

420 ppm is CO2 level of outside air.  800 ppm is maximum recommended indoors.

CO2 indoor monitor


How to improve

Open windows

Hepa filters

CO2 meter – $165

What Kind of HEPA Filter Unit Do You Need? –

Jeremy S. Faust, MD, attending physician in the Brigham and Women’s Hospital Department of Emergency Medicine, Division of Health Policy and Public Health, and instructor at Harvard Medical School. He is also the conductor and artistic director of The Longwood Chorus, an ensemble of health, medicine, and science professionals and students in the Boston area.”

Our Covid19 Resources playlist,